Magnetoresistive sensors provide a change of electrical resistance in response to changes in a magnetic field the sensor is exposed to. However, changes in other physical parameters, especially temperature, can also cause the electrical resistance of a magnetoresistive sensor to change. Traditionally, such drift effects have been alleviated by employing magnetoresistive sensors in an electrical bridge configuration. In this approach, a secondary magnetoresistive sensor is used as a reference, and sees the same environment as the primary magnetoresistive sensor, except that the secondary sensor is not exposed to the sample being measured. The differential signal between the primary and secondary sensors is a drift-compensated output signal.
However, recent applications of magnetoresistive sensors, such as biological assays, often require the use of a large array of magnetoresistive sensors. In such situations, the use of traditional drift compensation using an electrical bridge circuit is highly undesirable, since it entails the use of a separate reference detector (and associated bridge circuitry) for every element in the sensor array. Accordingly, methods of correcting for temperature and drift effects that don't rely on bridge circuits are of interest, especially for large sensor arrays.
One approach that has been considered is to control the temperature of the magnetoresistive sensor (e.g., as in U.S. Pat. No. 7,097,110). Elimination of temperature drift by controlling the temperature also leads to elimination of the temperature drift effect on sensor output. Another approach is to provide a temperature calibration of the sensor, such that sensor output is corrected according to measured temperature using the temperature calibration (e.g., as in U.S. Pat. No. 7,239,123).
However, conventional drift/temperature compensation approaches tend to suffer from various disadvantages. Some approaches are unduly complex or difficult to realize in practice. For example, temperature control can be difficult to realize for all elements of a large sensor array. Calibration approaches can also suffer from undue complexity, and/or an inability to provide corrected outputs in real time. Accordingly, it would be an advance in the art to provide improved drift/temperature correction for magnetoresistive sensors.